Automatic buff pressure setting

ABSTRACT

An improved control circuit for use with surface finishing machines having a driven surface finishing roll is adapted to establish and maintain desired working pressure relationships between the finishing roll and a workpiece.

United States Patent Weatherell 1*Mar. 26, 1974 1 1 AUTOMATIC BUFF PRESSURE SETTING [75] Inventor: James W. Weather-ell, Olean, NY. [56] References Cited UNITED STATES PATENTS [73] Asslgnee: Clair Mfg. Co., Inc., Olean, NY.

3,665,647 5/1972 Weatherell 51/45 Notice: The portion of the term of this 2,982,056 5/1961 Edqvist patent subsequent to May 30 1989 3,589,072 6/1971 Burt. 51/45 has been disclaimed.

Filed: Apr. 27, 1972 Appl. No.2 248,153

US. Cl. 51/33 R, 51/45, 51/165.9, 51/281 R Int. Cl B24b 1/00, B24b 49/08 Field of Search 51/2 K, 2 UA, 33 R, 34 R, 51/34 J, 45, 99, 281, 165.9, 47, 165.91, 165.92, 100, 92, 40, 39, 32

Primary ExaminerDona1d G. Kelly Attorney, Agent, or Firm-Bean & Bean 7 ABSTRACT An improved control circuit for use with surface finishing machines having a driven surface finishing roll is adapted to establish and maintain desired working I pressure relationships'between the finishing roll and a workpiece.

5 Claims, 7 Drawing Figures PATENIEDMARZS I974 3798.843

sum 2 or 2 AUTOMATIC BUFF PRESSURE SETTING BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to improvements in the automatic buff pressure setting control circuit disclosed by my co-pending application, Ser. No. 91,398, filed Nov. 20, 1970, now U.S. Pat. No. 3,665,647.

The control system disclosed in U.S. Pat. No. 3,665,647 is in turn an improvement over the control system disclosed by commonly assigned U.S. Pat. No. 3,589,072 for regulating movements of a finishing roll relative to a workpiece with a view to producing substantially uniform working pressure relationships between the finishing roll and the surface of the workpiece regardless of its contour.

More specifically, the control system of U.S. Pat No. 3,589,072 includes a fluid cylinder enclosing a movable piston coupled to the finishing roll in order to effect movement thereof towards and away from the workpiece; a balance control circuit for applying relatively high pressure air to the cylinder sufficient to counterbalance the weight of the finishing roll and to normally move same away. from the workpiece; a finishing roll pressure circuit for selectively applying relatively low pressure air to an opposite end of the cylinder in order to partially counterbalance the high pressure air and thereby permit a desired portion of the weight of the finishing roll to be applied as pressure to the workpiece; a reduced force circuit for effecting a decrease or reduction in the pressure or the low pressure air; and means to control operation of the reduced forced circuit in accordance with changes of profile of the workpiece surface.

The sluggishness or slow movement of the finishing roll towards the workpiece at the initiation of an operational cycle encountered with the control system of U.S. Pat. No. 3,589,072 was alleviated in accordance with the disclosure of U.S. Pat. No. 3,665,647 by momentarily interconnecting the counterbalance circuit with the finishing roll pressure control circuit in order to make available the full weight of the finishing roll for the purpose of driving the finishing roll downwardly into association with the workpiece; such interconnection being thereafter interrupted in order to maintain a desired work pressure relationship between the finishing roll and the surface of the workpiece.

While operation of the control circuit described in my co-pending application has been found to be completely satisfactory, it does however result in a bulky installation due to the provision of surge tanks in the circuits. Moreover, in that gravity alone is relied upon to initiate downward movement of the finishing roll, the rate of roll movement may vary from machine to machine as a result of differences in the amount of friction encountered in the finishing roll support bearings.

Thus the present invention is directed towards improvements in the control system disclosed by U.S. Pat. No. 3,665,647 with a view to simplifying and rendering same more compact, and for permitting adjustment of the rate of finishing roll downward movement, if required.

DRAWINGS The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein: Y

FIG. 1 is a front elevational view of the finishing machine in which the present invention has utility;

FIG. 2 is a left hand elevational view of the machine shown in FIG. 1;

FIG. 3 is a fragmentary sectional view taken generally along line 3-3 in FIG. 2;

FIG. 4 shows the control system of the present invention;

FIG. 4A is a sectional view taken generally along line 4A4A in FIG. 4;

FIG. 4B is a sectional view taken generally along line 4B-4B in FIG. 4; and

FIG. 5 is a schematic view illustrating a modified machine construction.

DETAILED DESCRIPTION It will be understood that the improved control system of the present invention, which is generally designated as 10 in FIG. 4, has utility in finishing machines or apparatus of the type shown by way of example and designated as 12 in accompanying FIGS. 1-3.

Reference to U.S. Pat. No. 3,589,072 and U.S. Pat. No. 3,665,647 may be held for a detailed description of the finishing machine 12. However, for reference purposes, finishing machine 12 will now be described as generally including a base formed from a pair of standards 20,20 arranged to support a bed plate 21 on which is supported a pair of upright pedestals 22,22 at its opposite sides. Pedestals 22,22 mount in vertically adjustable relation a pair of bearing blocks 25,25, which carry therebetween a horizontally disposed, nonrotatably mounted bridge shaft 26. Shaft 26 carries by means of stirrups 27,27 a rotatable lower shaft 28, which in turn supports arms 30, 32 and 33. Arms 30, 32 and 33 rotatably support drive shaft unit 34 for a finishing roll 35, which may be a grinding, abrading, brushing, polishing or buffing roll or the like, as may be required for any given instance of use. Drive shaft unit 34 is preferably driven by. an electric motor, not shown, through means of a belt 36, a pulley 37, an idler roll 38 riding freely on shaft 28, and a drive belt 39. An amp meter, not shown, is provided to appraise an operator of the load imposed on the finishing roll drive motor. 1

A carriage for mounting a workpiece to be processed is shown as generally including a platform 50, which is mounted on base plate 21 by means of slideways 52 for horizontal reciprocating movement in a direction transversely of roll 35 between pedestals 22. A hydraulic-piston cylinder unit 55 is mounted under base plate 21, such that its piston rod 56 extends in the direction of platform travel for connection with a bracket 57 depending from platform 50. Upright brackets 58 extend from the comer portions of platform 50 and support in a suitably elevated relation thereon a support table 60 on which workpieces 45 are to be disposed during the finishing operations. As will be apparent from viewing FIGS. 1 and 2, upon reciprocation of table 60 by means of cylinder 55, workpieces 45 will be passed back and forth beneath and in finishing contact with finishing roll 35. Also, it will be understood that the workpieces to be processed may either be in the form of flat sheet stock material, as indicated in FIG. 1, or be contoured, as indicated in FIG. 2. As

is conventional, the extent of reciprocation of platform 50 and thus table 60 may be readily controlled by means of mechanism, not shown, controlled by hand wheel 70. Also, as is conventional, machine 12 may include controls 80 for causing axial reciprocation of finishing roll 35 coincident with its rotation in order to avoid production of graining effects or the like on the finished surface of workpiece 45.

The elevational position of finishing roll 35 relative to a workpiece supported on table 60 may be regulated by means of the combination hand and pneumatic piston cylinder control unit 100, shown in FIGS. 2 and 4, which forms a part of control system 10, shown only in FIG. 4. Unit 100 includes a piston rod 102, which is threaded at one end thereof through a nut bearing 104, which is in turn carried by a crank arm 106 keyed for rotation with shaft 28. A hand wheel 108 is fitted to the upper end of rod 102 in order to facilitate manual adjustment thereof relative to nut bearing 104. At its lower-end rod 102 carries a piston head 110, which rides within fluid cylinder 112, mounted on the machine base, as by a pivot connection 114.

It will be understood that hand wheel 108 may be employed to make fine adjustments of the positioning of piston head 102 within cylinder 112 as required by slight variations in thickness of workpiece 45, whereas major adjustments may be made by adjusting table 60 relative to platform 50 by suitable means, not shown.

In an alternative control unit construction, which is designated as 100' in FIG. 5, a piston rod 102' is pivotally pin connected adjacent one end thereof to a crank arm 106, which in turn is keyed for rotation with shaft 28. The other end of piston rod 102 carries a piston head 110', which slides within fluid cylinder 112'. Cylinder 112' is supported relative to the machine base by means of a movable connection between its closed end and an adjustment rod 116; the latter being fitted with a hand wheel 117 and threadably received within a machine base mounted bearing block 118. Adjustments of rod 116 by means of hand wheel 117 may be employed to make fine adjustments of the relative positioning of piston head 110 and cylinder 112. If required, substantial changes in the thickness of workpieces may be accommodated by vertical adjustments of a workpiece transporting endless conveyor 119.

To adapt the machine illustrated in FIGS. 1 and 2 for processing workpieces having marked surface contour variations, there is provided a control unit generally designated as 120 in FIGS. 3, 4A and 43. Control unit 120 includes a pair of slide rods 122, which are fixed to platform 50, such as to extend lengthwise thereof in the direction of platform reciprocation. A plurality of control blocks 124 are slideably mounted on rails 122 for adjustment lengthwise thereof in order to permit the control blocks to be arranged substantially coincident with marked changes in contour of workpiece 45 in the manner best shown in FIG. 4. Each of control blocks 124 is provided with an operator or finger portion 126, which are set so as to extend alternately into registry with a pair of suitable sensors LS4 and LS5, which are positionally fixed to the base of machine 12. Thus, sensors LS4 and LS will be alternately actuated by operators 126 substantially coincident with the change in contour of the workpiece being reciprocated relative to finishing roll 35.

Now referring specifically to FIG. 4, it will be understood that control system 10 generally includes a plurality of fluid circuits including a counterbalance circuit 130; a work pressure control circuit a reduce force circuit a roll lowering or coupling circuit and previously mentioned finishing roll reciprocation control 80. Control 80 is boxed by dashed lines in order to indicate that it may be removed from the system in cases where reciprocating movements of the finishing roll are not required. In a like manner, reduced force circuit 150 is boxed by dashed lines for the purpose of indicating that it may be removed from the control system when the finishing machine is only intended for use in finishing flat sheet stock.

Counterbalance circuit 130 is shown as including a manually adjustable pressure regulator 162, which con trols passage of air under pressure relatively high through a conduit 163 to a valve 164, the air subsequently being directed to the upper end of cylinder 112 through line 166 having as required a suitable flow control valve 168. Valve 164 is characterized as having a cavity 1640 into which lines 163 and 166 and an atmospheric exhaust port 164b are connected; a flexible, generally disc-shaped diaphragm 1640 being loosely fitted within cavity 164a for the purpose of controlling communication between lines 163 and 166 and exhaust port 164b. In this respect, when the pressure of the air within line 163 exceeds the pressure within the upper part of cylinder 110, diaphragm 1641; is forced to seal port 164b and its edges are slightly bent to permit flow of air from line 163 to line 166. When the pressure within the upper end of cylinder 110 tends to exceed a predetermined pressure, which essentially corresponds to the pressure within line 163, the diaphragm is raised to seal line 163 and connect line 166 with port l64b. This operation of valve 164 insures that a predetermined high pressure is continuously maintained in i the upper end of cylinder 110, while permitting upwardly movements of piston head 110, as required to permit lowering of roll 35 into engagement with the workpiece in the manner to be hereinafter described.

Work pressure control circuit 140 is shown as including a manually adjustable pressure regulator 172 through which air under relatively low pressure is passed to a normally closed two-way valve 174 under the control of a solenoid 175 and subsequently to the lower end of cylinder 112 through line 176, a dual pressure shuttle valve 178, line 180, valve 182 and line 184. As required, a suitable flow control valve 186 may be disposed in line 184 between valve 182 and the lower end of the cylinder. It will be understood that valve 182 is identical in construction to valve 164 and includes a cavity 182a, an atmospheric exhaust port 182b and a diaphragm 1820 for alternatively blocking line and port l82b in a manner determined by the relative pressures in lines 180 and 184. Valve 178 is also similar to valve 164 in that it includes a chamber 178a, a port l78b and a diaphragm 1780. However, port 178b serves to interconnect the work pressure control circuit with coupling circuit 160 in the manner to be-described, rather than being continuously connected to the atmosphere.

Reduced force circuit 150 is shown as including a line 192, which is branched from line 184, a two-way valve 194, and line 196, which opens to the atmosphere through a manually adjustable throttle valve 198. It will be understood that two-way valve 194 includes a solenoid operator 199, whose condition is determined by which of sensors LS4 and LS5 have been most recently engaged by one of operator fingers 126. Thus, two-way valve 194 is in closed condition subsequent to operation of sensor LS5, but before operation of sensor LS4, whereas the valve is in its open condition subsequent to operation of sensor LS4, but before operation of sensor LS5. it will be understood that solenoid operator 199 is deenergized to permit valve 194 to remain in a normally closed, flow blocking condition, during processing of moderately contoured or flat sheet stock material or during periods of operation during which the tinishing roll is permitted to move down an incline, such as for instance between points 2-3 and 4-5 shown in FIG. 5.

Coupling circuit 160 includes a line 202, which is branched from line 163; a. normally closed two-way valve 204 controlled by a solenoid operator 206; a line 208; an adjustable time delay valve 2l0;and a line 212 connecting into a valve port 178b. Valve 210 is a normallyopen, time closed valve, which is resettable to open position by a surge of air passing through line 208 upon opening of valve 204; valve 210 when closed serving both to block line 208 and to vent line 212 to the atmosphere. By adjustments of valve 210 the period of time during which relatively high pressure air is applied at port l78b may be accurately controlled.

in the preferred form of the invention solenoids 175 and206 are connected in parallel such that valves 174 and 204 are simultaneously opened upon initiation of operation of the machine by depression of a control button or foot pedal, not shown. However, as will be apparent, this arrangement employing the pneumatic time control afforded by valve 210 may be replaced by an electrically operated timer of the type disclosed in my copending application.

Control 80.includes an adjustable pressure regulator 220, which controls passage of air to a four-way double solenoid operated valve 222; valve 222 serving to alternately supply air and exhaust to atmosphere opposite ends of a cylinder 224 in order to effect reciprocations of the processing roll.

Finishing machine 12 is initially set up by adjusting hand wheel 108 to insure that piston head 110 will not abut against the upper end of cylinder 112 when finishing roll 35 is fully worn and in its full down position. Thereafter, the operator will adjust regulator 162 in order to apply'high pressure air to the upper end of cylinder 112, which is slightly above that necessary to balance or compensate for the weight of the finishing roll, such that piston head 110 is biased downwardly within cylinder 112 and the finishing roll raised into its phantom line position shown in FIG. 4- Wit a machine of the type illustrated in FIGS. 1 and 2, and the finishing roll being in the form of a conventionally sized buffing roll, a raise roll pressure of about 40 psi is normally employed.

Setting of regulator 162 is carried out with valves 174 and 204 in their normally closed conditions, such as to block passage of air to shuttle valve 178, and to vent the lower end of cylinder 112 to atmosphere through valve port l82b.

Thereafter, the operator initially adjusts work pressure regulator 172 to apply a pressure of normally between about and psi to line 176. The operator then activates the machine start button, which effects energization of solenoids 175 and 206 by means of suitable circuitry, not shown. As a result, high pressure air is immediately passed from branch line 202 through valve 204, line 208, valve 210, line 212, valve 178, line 180, valve 182 and line 184 into the lower end of cylinder 112, whereupon the air pressure across piston head is substantially equalized and the full weight of roll 35 permitted to initiate movement of the finishing roll downwardly into engagement with workpiece 45. Concurrently, work pressure line 1.76 is closed by diaphragm 1780, since the pressure in line 212 is substantially in excess of that in line 176; and pressure in the upper end of cylinder 112 is maintained essentially constant by venting through valve 164. immediately thereafter, that is normally within about one second, the time delayed device associated with valve 210 closes line 208 and vents line 212 to the atmosphere, whereupon lines 180 and 212 are exhausted to atmosphere through valve 210 and line 184 is exhausted to the atmosphere through valve 182. As the pressure in lines 180 and 184,- and thus the lower end of cylinder 112 falls to about the 10-20 psi work pressure in line 176, diaphragms 178C and 1826 are substantially immediately forced to close off their associated ports 178b and 182b and place lines 176, 180 and 184 in communication in order to establish and maintain the desired work pressure in the lower end of cylinder 112. Operation of the valves 178, 182 and 210 is such that work pressure is normally applied tothe lower end of cylinder 112 before the finishing roll is forced upwardly from engagement with the workpiece by the 40 psi raise pressure continuously present in the upper end of the cylinder 112, during the above described operation. It will be understood that the application of high pressure air to the lower end of the cylinder is preferably only momentary, that is, only of sufficient duration to permit the unbalanced weight of the finishing roll to initiate movement thereof towards the workpiece. The almost immediate reduction of the pressure in the lower end of the cylinder to the previously set work pressure thereafter serving to cushion contact between the falling finishing roll and the workpiece in order to prevent any damage to the latter.

Regulator 172 is then manually adjusted by the operator to vary the work pressure, as determined by visual inspection of the finish produced on the surface of the workpiece. When the workpiece is flat sheet material or only slightly contoured the above operations complete setting of the machine. When, during a subsequent processing operation, a slight variation in contour of the workpiece tends to force roll 35 upwardly and thus piston head 110 downwardly within cylinder 1 12, valve 182 serves to exhaust the lower end of cylinder 112 to atmosphere sufficiently to retain the working pressure therewithin at an essentially constant level. Of course, when a workpiece has substantial contour variations, it will be necessary to employ circuit in the manner to be described.

Finishing roll 35 may be raised to its phantom line position, shown in FIG. 4, whenever it is desired to remove or introduce a workpiece by deenergizing solenoids and 206 so as to return valves 174 and 204 to their initial conditions, wherein line 184 is vented to the atmosphere. Preferably, valve 178 is disposed in an inverted position relative to that shown.

It will be understood that after regulator 172 has been set by the operator to provide a desired surface finish, substantially identical pressure will be subsequently maintained on the workpiece regardless of the degree of wear to which finishing roll 35 is subjected. This is to be compared with arrangements, wherein continued adjustment of hand wheel 108 was necessary to compensate for wear of the finishing roll. Setting up of the finishing machine to accommodate in irregularly shaped workpieces, i.e., those having vertical inclines of more than about 30, is identical to that described above, except that during the final adjustment of work pressure regulator the operator makes a note of the work performed by the finishing roll driving motor, not shown, as indicated by an asosciated amp meter, also not shown. In this respect, it will be understood that the amp meter reading of the drive motor will remain substantially constant when the finishing roll is processing either a flat workpiece or moving down an inclined surface of a contoured workpiece, ie. between points 2-3 and 4-5 in FIG. 4, due to the fact that work pressure is maintained at a constant value. However, when the finishing roll is forced to move up an incline of greater than about 30 ie. between points I-2 and 3-4 in FIG. 4, it has been observed that the finishing roll tends to dig into the workpiece, such that the workpiece is finished to a greater extent than desired and the drive motor is subjected to an increased load. Thus, when setting up for workpieces having a pronounced contour, the operator adjusts the trottle valve 198, when two way valve 194 is in its open condition to'bleed air off from the lower end of cylinder 112 in an amount necessary to obtain an amp meterreading identical to that previously observed in the initial setting up of the work pressure. 1

During operation, solenoid 194 will normally remain deenergized in order to maintain two way valve 194 in its normally closed condition. When sensor LS4 is engaged by an operator finger 126, solenoid 199 is operated to place two way valve 194 in its open condition and permit a desired amount of air to bleed off to atmosphere as determined by the setting of throttle valve 198. As a result, finishing roll 35 is freed to permit movement thereof up the incline without performing excessive finishing action on the workpiece. Coincident with the positioning of the finishing roll at the top of the incline, an operator finger 126 is positioned in engagement with sensor LS5 to effect deenergization of solenoid 199 and the resultant closing of two way valve 194. Simultaneously therewith, the normal work pressure is reapplied to the lower end of cylinder 112 in order to force finishing roll 35 to move down the incline while exerting the desired work pressure. Opening and closing of two way valve 194 will continue as determined by the preset positioning of operator finger 126. Of course, it will be understood that the location of operator fingers 126 may be adjusted as desired to provide for a desired lead and lag operation of the pressure control system and that the pressure bleed off and buildup sequences may be readily regulated as to timing and degree, so as to accommodate for finishing of any irregularly or regularly contoured workpiece.

It should be noted that the bearing friction present in the finishing roll mounting is normally such that some value less than the actual weight of the finishing roll is available for initiating its downward movement, and that the amount of friction may vary substantially between machines. Accordingly, with a view to overcoming any sluggishness in downward movement of the finishing roll and permitting uniformity of such movement between machines, the above described roll lowering circuit may be modified by deleting branch line 202 and connecting valve 204 to a high pressure source through adjustable pressure regulator 220 and line 222, as indicated in phantom line in FIG. 4. Regulator 222 would be adjustably set at some value higher than the pressure setting of regulator 162, such that at the initiation of an operational cycle the pressure of air introduced into the lower end of cylinder 112 would be in excess of that supplied to its upper end, as required to compensate for frictional losses. Of course, if extremely rapid finishing roll movement is required, the setting of regulator 220 may be increased over that necessary to compensate for frictional losses.

I claim: I

1. In a'workpiece surface finishing apparatus including a base, means to support a workpiece on said base, a finishing roll mounted on said base for movement towards and away from said workpiece between a first position and a second workpiece engaging position, and a control system regulating movement of said finishing roll relative to said workpiece, the improvement wherein said control system comprises in combination:

a fluid cylinder,

a piston movable relatively within said cylinder, one of said cylinder and piston being fixed to said base and the other thereof being coupled to said roll, said piston when movable in one direction relative to said cylinder tending to raise said roll upwardly away from said workpiece into said first position and when movable in an opposite direction permitting the weight of said roll to move same into said second position;

a counterbalance circuit for continuously applying air at a relatively high pressure to one end of said cylinder, said high pressure air tending to counterbalance the weight of said roll and to move said piston in said one direction, said circuit means including valve means for venting said one end of said cylinder to the atmosphere whenever pressure in said one end exceeds that of said high pressure air; and

other circuit means operable in succession for venting an other end of said cylinder to atmosphere whereby to permit said high pressure air applied to said one end of said cylinder to maintain said roll in said first position, for introducing air at a pressure at least equal to said high pressure into said other end of said cylinder whereby to substantially counterbalance said high pressure air continuously applied to said one end of said cylinder to permit substantially the full weight of said roll to initiate movement thereof from said first into said second position, for reducing the pressure of air applied to said other end of said cylinder to a relatively low pressure whereby to partially counterbalance said high pressure applied to said one end of said cylinder such that the difference between said high and low pressures determines the pressure of said roll on said workpiece when in said second position and for venting said other end of said cylinder to the atmosphere whenever pressure in said other end exceeds said low pressure.

2. In a workpiece surface finishing apparatus including a base, means to support a workpiece on said base,

a finishing roll mounted on said base for movement towards and away from said workpiece between a first position and a second workpiece engaging position, and a control system regulating movement of said finishing roll relative to said workpiece, the improvement wherein said control system comprises in combination:

a fluid cylinder;

a piston movable relatively within said cylinder, one of said cylinder and piston being fixed to said base and the other thereof being coupled to said roll, said piston when movable in one direction relative to said cylinder tending to raise said roll upwardly away from said workpiece into said first position and when movable in an opposite direction permitting the weight of said roll to move same into said second position;

a counterbalance circuit including a source of air under relatively high pressure and first connecting means connected into one end of said cylinder for continuously applying high pressure air from said high pressure source to said one end of said cylinder, said high pressure air tending to counterbalance the weight of said roll and to move said piston in said one direction, said counterbalance circuit means including valve means for venting said one end of said cylinder to the atmosphere whenever pressure in said one end exceeds said high pressure;

a finishing roll pressure control circuit including a source of air under relatively low pressure and second connecting means connected into another end of said cylinder, said second connecting means having a second valve means for selectively blocking said low pressure source and third valve means downstream of said second valve means for venting said other end of said cylinder to atmosphere whenever pressure in said other end of said cylinder exceeds pressure in said second connecting means upstream of said third valve means, whereby to permit said high pressure air applied to said one end of said cylinder to maintain said roll in said first position when, said low pressure. source is blocked by said second valve means, said second connecting means when said low pressure source is unblocked by said second valve means normally connecting said lower pressure source to said other end of said cylinder, said low pressure air when applied tending to partially counterbalance said high pressure air applied to said one end of said cylinder such that the difference in pressure between said high pressure air and low pressure air determines the pressure of said finishing roll on said workpiece when in said second position; and

a finishing roll lowering circuit including a source of air under pressure at least as high as said high pressure and third connecting means for momentarily coupling the last said source'of air under pressure to said second connecting means intermediate said 7 second and third valve means thereby to momentarily apply air from the last said source to said other end of said cylinder to substantially counter-' tion. v

3. The improvement according to claim 2, wherein the last said source supplies air at a pressure in excess of said high pressure.

4. The improvement according to claim 2, wherein said third connecting means includes fourth and fifth valve means, said fourth valve means being arranged intermediate the last said source and said fifth valve means and acting to block and unblock the last said source conjunctively with the blocking and unblocking of said low pressure source by said second valve means, said fifth valve means blocking the last said source and venting said third connecting means downstream of fifth valve means to atmosphere after a time delay following unblocking of the last said source by said fourth valve means, and said third connecting means is connected into said second connecting means downstream of said fifth valve means by a dual pressure shuttle valve operable to place said third connecting means in flow communication with said second connecting means downstream of said shuttle valve whenever air pressure in said third connecting means exceeds air pressure in said second connecting means upstream of said shuttle valve or air pressure in said second connecting means downstream of said shuttle valve exceeds air pressure in said second connecting means upstream of said shuttle valve and said third connecting means downstream of said fifth valve means is vented to atmosphere.

5. A method of lowering a finishing roll into contact with a workpiece and thereafter maintaining a substantially uniform pressure relationship between said finishing roll and said workpiece comprising the steps of:

coupling a fluid cylinder-piston'unit to said finishing roll such that movement of its piston in one direction relative to its cylinder tends to raise said roll upwardly away from said workpiece into a first position remote therefrom, whereas relative movement of said piston in an opposite direction permits the weight of said roll to move same into a second workpiece engaging position;

continuously introducing relatively high pressure air into one end of said cylinder whereby to move said piston in said one direction and normally maintain said roll in said first position thereof, while venting said one end to atmosphere whenever pressure in said one end exceeds said relatively high pressure;

momentarily introducing air into an other endof said cylinder at sufficiently high pressure to at least substantially balance air pressure across said piston thereby to permit substantially the full weight of said roll to initiate movement thereof towards said second position; and

reducing said sufficiently high pressure applied to said other end of said cylinder to a relatively low pressure during the period of movement of said roll toward and into said second position and thereafter venting said other end to atmosphere whenever pressure in said other end exceeds said relatively low pressure, the difference between said continuously introduced relatively high and relatively low pressures determining the working pressure between said roll and said workpiece. 

1. In a workpiece surface finishing apparatus including a base, means to support a workpiece on said base, a finishing roll mounted on said base for movement towards and away from said workpiece between a first position and a second workpiece engaging position, and a control system regulating movement of said finishing roll relative to said workpiece, the improvement wherein said control system comprises in combination: a fluid cylinder; a piston movable relatively within said cylinder, one of said cylinder and piston being fixed to said base and the other thereof being coupled to said roll, said piston when movable in one direction relative to said cylinder tending to raise said roll upwardly away from said workpiece into said first position and when movable in an opposite direction permitting the weight of said roll to move same into said second position; a counterbalance circuit for continuously applying air at a relatively high pressure to one end of said cylinder, said high pressure air tending to counterbalance the weight of said roll and to move said piston in said one direction, said circuit means including valve means for venting said one end of said cylinder to the atmosphere whenever pressure in said one end exceeds that of said high pressure air; and other circuit means operable in succession for venting an other end of said cylinder to atmosphere whereby to permit said high pressure air applied to said one end of said cylinder to maintain said roll in said first position, for introducing air at a pressure at least equal to said high pressure into said other end of said cylinder whereby to substantially counterbalance said high pressure air continuously applied to said one end of said cylinder to permit substantially the full weight of said roll to initiate movement thereof from said first into said second position, for reducing the pressure of air applied to said other end of said cylinder to a relatively low pressure whereby to partially counterbalance said high pressure applied to said one end of said cylinder such that the difference between said high and low pressures determines the pressure of said roLl on said workpiece when in said second position and for venting said other end of said cylinder to the atmosphere whenever pressure in said other end exceeds said low pressure.
 2. In a workpiece surface finishing apparatus including a base, means to support a workpiece on said base, a finishing roll mounted on said base for movement towards and away from said workpiece between a first position and a second workpiece engaging position, and a control system regulating movement of said finishing roll relative to said workpiece, the improvement wherein said control system comprises in combination: a fluid cylinder; a piston movable relatively within said cylinder, one of said cylinder and piston being fixed to said base and the other thereof being coupled to said roll, said piston when movable in one direction relative to said cylinder tending to raise said roll upwardly away from said workpiece into said first position and when movable in an opposite direction permitting the weight of said roll to move same into said second position; a counterbalance circuit including a source of air under relatively high pressure and first connecting means connected into one end of said cylinder for continuously applying high pressure air from said high pressure source to said one end of said cylinder, said high pressure air tending to counterbalance the weight of said roll and to move said piston in said one direction, said counterbalance circuit means including valve means for venting said one end of said cylinder to the atmosphere whenever pressure in said one end exceeds said high pressure; a finishing roll pressure control circuit including a source of air under relatively low pressure and second connecting means connected into another end of said cylinder, said second connecting means having a second valve means for selectively blocking said low pressure source and third valve means downstream of said second valve means for venting said other end of said cylinder to atmosphere whenever pressure in said other end of said cylinder exceeds pressure in said second connecting means upstream of said third valve means, whereby to permit said high pressure air applied to said one end of said cylinder to maintain said roll in said first position when said low pressure source is blocked by said second valve means, said second connecting means when said low pressure source is unblocked by said second valve means normally connecting said lower pressure source to said other end of said cylinder, said low pressure air when applied tending to partially counterbalance said high pressure air applied to said one end of said cylinder such that the difference in pressure between said high pressure air and low pressure air determines the pressure of said finishing roll on said workpiece when in said second position; and a finishing roll lowering circuit including a source of air under pressure at least as high as said high pressure and third connecting means for momentarily coupling the last said source of air under pressure to said second connecting means intermediate said second and third valve means thereby to momentarily apply air from the last said source to said other end of said cylinder to substantially counterbalance said high pressure air continuously applied to said one end of said cylinder to permit substantially the full weight of said roll to initiate movement thereof from said first into said second position.
 3. The improvement according to claim 2, wherein the last said source supplies air at a pressure in excess of said high pressure.
 4. The improvement according to claim 2, wherein said third connecting means includes fourth and fifth valve means, said fourth valve means being arranged intermediate the last said source and said fifth valve means and acting to block and unblock the last said source conjunctively with the blocking and unblocking of said low pressure source by said second valve means, said fifth valve means blocking the last said source and Venting said third connecting means downstream of fifth valve means to atmosphere after a time delay following unblocking of the last said source by said fourth valve means, and said third connecting means is connected into said second connecting means downstream of said fifth valve means by a dual pressure shuttle valve operable to place said third connecting means in flow communication with said second connecting means downstream of said shuttle valve whenever air pressure in said third connecting means exceeds air pressure in said second connecting means upstream of said shuttle valve or air pressure in said second connecting means downstream of said shuttle valve exceeds air pressure in said second connecting means upstream of said shuttle valve and said third connecting means downstream of said fifth valve means is vented to atmosphere.
 5. A method of lowering a finishing roll into contact with a workpiece and thereafter maintaining a substantially uniform pressure relationship between said finishing roll and said workpiece comprising the steps of: coupling a fluid cylinder-piston unit to said finishing roll such that movement of its piston in one direction relative to its cylinder tends to raise said roll upwardly away from said workpiece into a first position remote therefrom, whereas relative movement of said piston in an opposite direction permits the weight of said roll to move same into a second workpiece engaging position; continuously introducing relatively high pressure air into one end of said cylinder whereby to move said piston in said one direction and normally maintain said roll in said first position thereof, while venting said one end to atmosphere whenever pressure in said one end exceeds said relatively high pressure; momentarily introducing air into an other end of said cylinder at sufficiently high pressure to at least substantially balance air pressure across said piston thereby to permit substantially the full weight of said roll to initiate movement thereof towards said second position; and reducing said sufficiently high pressure applied to said other end of said cylinder to a relatively low pressure during the period of movement of said roll toward and into said second position and thereafter venting said other end to atmosphere whenever pressure in said other end exceeds said relatively low pressure, the difference between said continuously introduced relatively high and relatively low pressures determining the working pressure between said roll and said workpiece. 